Abstract
Grassland bird populations have declined more than any other group of bird species in North America. Some species such as the grasshopper (Ammodramus savannarum) and Baird’s sparrows (Ammodramus bairdii) are of particular conservation concern, since they have shown negative trends in their population over the last 50 years. Their winter ecology has only begun to be studied recently and information is limited. The purpose of this study is to achieve the morphometric characterization of these two grassland species during the wintering season. The study is conducted in the Rancho Santa Teresa located in Villa Hidalgo, Durango, Mexico and the Ecological reserve “El Uno”, located in Janos, Chihuahua, Mexico. During winter 2013-2014, 135 birds were captured; banded and zoometric measurements were taken such as total body weight, wing chord, tail length, culmen, and beak depth and width. Two indices of body condition (BCI) are also calculated. All measurements and indices are compared per species and per sex. Both species are sexed with molecular techniques, determining 20 females and 18 males for A. bairdii and 41 females and 56 males for A. savannarum. All variables are significant different between species (p A. bairdii (p p p A. bairdii. The biometric data obtained in this study can be used as reference values wintering populations of both species.
Highlights
Land use conversion and ecological drivers’ alteration in North American grasslands [1] have generated a decrease in the populations of grassland birds, more evident than for any other group of birds [2]
Study Area The study was conducted in two areas (Figure 1) during the winter season of 2013-2014 in two Grasslands Priority Conservation Areas (GPCAs) of the Chihuahua Desert; the first one in the Santa Teresa Ranch located in the northwestern state of Durango (26 ̊18'03"N, 105 ̊09'41"W) in the region of Cuchillas de la Zarca, vegetation consists of xeric scrub, and natural grasslands, where the shrub layer consisted of the genera: Prosopis, Acacia, Juniperus and Quercus, the herbaceous layer consisted of genera: Bouteloa, Aristida and Hilaria [14]
It is observed that the variable weight was different for both species and approaches the values published by other authors, who report for A. bairdii values of 17.5 ± 1.34 g with a range of 15.0 - 20.3 g [20] [21] and for A. savannarum 17.0 ± 2.75 g for both sexes [6] [21] with data obtained from breeding areas
Summary
Land use conversion and ecological drivers’ alteration in North American grasslands [1] have generated a decrease in the populations of grassland birds, more evident than for any other group of birds [2]. Ammodramus bairdii breeds in southern Canada and northern United States and winters in Arizona, New Mexico and Texas in the US, and Chihuahua, Sonora, Durango and Coahuila in Mexico [5], whereas A. savannarum has a wider range, breeding from southern Canada, largely from the United States and northern Mexico [6] Baird’s sparrow has a tail fairly short and spiky, crown flattish, bill flesh with dusky culmen, legs flesh. The face of this sparrow shows an ochraceous buff with black moustache and two dark corner marks on hind auriculars. The tail feathers are dark brown with paler edgings, outer rectricesare paler [7]
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